Rod guide for rotating rod strings

ABSTRACT

A rod guide for installation on an intermediate section along a rod without need for access to ends thereof, and which provides a synthetic, low friction surface for reduced contact to either the guide or surrounding tubing. The rod guide has a robust construction for secure attachment to the rod, yet is characterized by ease of installation and replacement. Various outer profiles of low friction surface can be employed, and the low friction surface can be replaced without removing the entire rod guide. Each rod guide can be installed periodically along a rod such as through a work window installed above blow out preventer (BOP) or pack-off element.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims benefit of U.S. provisional patent application Ser. No. 62/158,200, filed on May 7, 2015, the content of which is incorporated herein by reference in its entirety.

FIELD

Embodiments described herein relate to rod guides for rod strings, more particularly for rotating rods without axial access for rod guide installation.

BACKGROUND

Progressive cavity (PC) pumps are located downhole in a wellbore, the rotor of which is rotatably driven using a rod string extending from surface to the downhole pump. The rod strings transfer torque to the rotor and support axial loads, namely the weight of the rod string plus the thrust load applied by the pump. Rod string configurations include a plurality of standard lengths of sucker rods coupled together to form the rod string. More recently the rod string can be formed of continuous rod such as COROD®, a trademark of Weatherford Technology Holdings, LLC.

PC pumps are typically installed at the end of production tubing. In horizontal well scenarios, in both heel and horizontal portions of the wellbore, the rotation of the rod string within the production tubing can cause wear to both the rod string and the production tubing.

With a plurality of sucker rods, it is known to apply one of many forms of rod guides that can be installed on each length of rod as it is coupled to the next rod. A male end of the sucker rod receives the rod guide, before threaded coupling of upsets on the male ends to female threads in couplings used for connection to the next length of sucker rod and so on, as a rod string of hundreds of rods and thousands of feet in overall length is assembled.

With continuous rods it is suggested that, absent the couplings, wear is substantially eliminated and rod guides are not required. Further, as the rod is indeed continuous, it is impractical to fit conventional tubular rod guides at intermediate locations along the rod from one end, there being only one accessible end, which is only accessible upon first insertion into the production tubing. Nevertheless, some operators have noted that the axial tension in the rod string draws the string up to wear against and to wear the uphole side wall of the production tubing of the heel section in a horizontal wellbore. Thus rod guides are desirable, if only at that part of the well. With PC pumps lasting up to 2 years in operation before servicing, the wear to the rod and to the tubing can be significant.

There have been attempts to mitigate continuous rod wear including surface tubing rotators and downhole swivel joints to distribute wear and two-piece rod guides that are akin to clamp or split muff couplings used to join shafts. The split configuration permits periodic installation whilst the rod ends are unreachable. Namely, such a configuration permits installation intermediate the rod string without access to either end. The rod guides are strategically installed only along the portions of the continuous rod adjacent the heel. Such rod guides are at least partially fit with plastic surfaces or implement a rotatable configuration to lessen contact wear with the heel portion of the production tubing. The split couplings have implemented cap screws or other fasteners to secure the pieces together. To date however, the tubing rotator/swivel and split rod guides have proven troublesome to install, have a high failure rate and are overall unsatisfactory.

SUMMARY

Herein, a rod guide is provided that can be installed on an intermediate section along a rod without need for access to ends thereof and provides a synthetic, low friction surface for reduced contact to either the guide or surrounding tubing. The rod guide has a robust construction for secure attachment to the rod, yet is characterized by ease of installation. Each rod guide can be installed periodically along a rod such as through a work window installed above blow out preventer (BOP) or pack-off element. During run in of a string of PC pump's continuous rod into production tubing, wellbore pressure can be controlled, and the work window can be opened for access to the continuous rod for guide installation.

According to one aspect, there is provided a rod guide for installation on a rod string comprising: a tubular clamp having an inner rod bore and an outer bearing surface about an axis and having an axial height, the clamp being split diametrically along a first separation plane through the rod bore to form a first clamshell clamp portion and a second clamshell clamp portion, the first separation plane extending along the rod bore at an angle to the axis and passing through the axis intermediate the axial height for forming a pair of radial wall faces extending axially along the height of each of the first and second clamshell clamp portions; and interlocking clamp profiles along at least a portion of each of the wall faces and complementary between the first and second clamshell clamp portions for radially securing the clamshell clamp portions together.

In one embodiment, there is also provided a bushing having an inner bushing bore fit to the clamp's outer bearing surface and an outer wear surface and having an axial height, the bushing being split diametrically along a second separation plane through the inner bushing bore to form a first clamshell bushing portion and a second clamshell bushing portion, the second separation plane extending along the inner bushing bore for forming a pair of radial bushing wall faces extending axially along the height of each of the first and second clamshell bushing portions; and interlocking bushing profiles along at least a portion of each of the bushing wall faces and complementary between the first and second clamshell bushing portions for radially securing the clamshell bushing portions together.

In one embodiment, each interlocking clamp profile comprises a complementary dovetail tongue and slot.

In one embodiment, each of the pair of wall faces of the first clamshell clamp portion comprises a tongue along at least a portion of its height, and each of the pair of wall faces of the second clamshell clamp portion comprises a slot along its height, the tongues being axially slidable along the slots and complementary for locking the clamshell clamp portions together radially.

In one embodiment, each interlocking bushing profile comprises a complementary circular bushing tongue and bushing slot.

In one embodiment, each of the pair of bushing wall faces of the first clamshell bushing portion comprises a bushing tongue along at least a portion of its height, and each of the pair of bushing wall faces of the second clamshell bushing portion comprises a bushing slot along its height, the bushing tongues being axially slidable along the bushing slots and complementary for locking the clamshell bushing portions together radially.

In one embodiment, each of the pair of bushing wall faces of the clamshell bushing portions comprises a bushing tongue along at least a portion of its height and a bushing slot along its height, the bushing tongues being axially slidable along the bushing slots and complementary for locking the clamshell bushing portions together radially.

In one embodiment, the first separation plane angle is self-locking.

In one embodiment, the first separation plane angle is greater than about 2 degrees and less than about 16 degrees.

In one embodiment, the first separation plane angle is between about 5 to about 6 degrees.

In one embodiment, the second separation plane is parallel to, and along, the axis of the bushing bore.

In one embodiment, the second separation plane is at an angle to the axis and passes through the axis intermediate an axial height of the bushing.

In one embodiment, the second separation plane angle is self-locking.

In one embodiment, the bushing is made of a low friction polymer.

In one embodiment, at least one of the clamshell clamp portions comprise a flange at a first end.

In one embodiment, one of the clamshell clamp portions is of a greater height than the opposing clamshell clamp to form an axially offset retaining structure at a second end and having slots formed therein to receive a retainer and sandwich the bushing between the flange and the retainer.

In one embodiment, the retainer is a C-shaped retainer.

In one embodiment, the retaining structure and retainer each include one or more complementary pinholes for receiving retaining pins.

In one embodiment the one or more pinholes of the retaining structure are smaller in diameter than the one or more pinholes of the retainer.

In one embodiment, the bushing is rotatable about the clamp.

In one embodiment, there is provided a bushing having an inner bushing bore fit to the clamp's outer bearing surface and an outer wear surface, wherein the bushing is bonded to the clamp's outer bearing surface.

In one embodiment, at least one clamp groove runs axially along the outer bearing surface of the clamp and at least one bushing spline complementary to the at least one clamp groove runs axially along the inner bushing bore.

In one embodiment, a plurality of bushing ribs extend generally axially along the outer wear surface of the bushing.

According to one aspect, there is provided a method for securing a rod guide to a string of rod, comprising locating a first clamshell clamp portion about the rod; locating a second clamshell clamp portion in opposing relation about the rod, the first and second clamshell clamp portions having an inner bore and interlocking interfaces along a first separation plane through the inner bore, the first separation plane at an angle to the rod's axis; arranging a first end of one of the first or second clamshell clamp portions with an opposing end of the other of the second or first clamshell clamp portion; aligning the interlocking interfaces of the respective interlocking interfaces of the first or second clamshell clamp portions; axially and slidably coupling the first and second clamshell clamp portions until the first or second clamshell clamp portions clamp to the rod.

In one embodiment, said securing a rod guide to a string of rod further comprises locating a first clamshell bushing portion about the outer bearing surface of the first and second clamshell clamp portions; locating a second clamshell bushing portion in opposing relation about the first and second clamshell clamp portions; coupling the first and second clamshell bushing portions; and axially restraining the first and second clamshell bushing portions to the first and second clamshell clamp portions.

In one embodiment, said securing a rod guide to a string of rod further comprises using a striking tool to strike one of the first or second clamshell clamp portions to axially and slidably couple the first or second clamshell clamp portion with the second or first clamshell clamp portion.

In one embodiment, the axially retaining step of said securing a rod guide to a string of rod further comprises sandwiching the first and second clamshell bushing portions between a flange and a retainer by inserting a retainer into a retaining structure of the first or second clamshell clamp portion and aligning a one or more retaining pin holes of the retaining structure with a one or more pin holes of the retainer to secure the clamshell bushing portions to the clamp.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a progressive cavity pump located downhole in a horizontal wellbore and connected to surface via a rod string, with a plurality of rod guides installed through a work window at surface to the rod;

FIG. 2A is a side view of a rod guide installed on the rod string;

FIG. 2B is a top view of a rod guide installed on the rod string;

FIG. 3A is a side view of the clamp portion of the rod guide with a cut line indicating where the clamshell portions of the clamp interface;

FIG. 3B is an axial view of the clamp portion of the rod guide from one end;

FIG. 3C is an axial view of the clamp portion of the rod guide from the other end;

FIG. 4 is an axial view of the clamp portion of the rod guide from both ends, with an transverse cross-sectional view of the rod string;

FIG. 5A is a perspective view of the male clamshell of the clamp;

FIG. 5B is a perspective view of the female clamshell of the clamp;

FIG. 6A is a perspective view of the clamp depicting the interface between the clamshell sections, the plane of separation being aligned along a normal to the sheet;

FIG. 6B is a close-up view of one of the interfaces between the clamshells of the clamp;

FIG. 7A is an axial plan view of one clamshell of the bushing portion of the rod guide;

FIG. 7B is a close-up view of one of the interfaces between the clamshells of the bushing;

FIG. 8A is a top plan view of the assembled rod guide;

FIG. 8B is a cross-sectional view of the assembled rod guide;

FIG. 9A is a side view of the assembled rod guide, showing a C-shaped retainer inserted into a retaining structure of the clamp and a retaining pin inserted into the retaining structure and C-shape retainer;

FIG. 9B is a side view of the assembled rod guide, showing a C-shaped retainer inserted into the retaining structure of the clamp;

FIG. 9C is a top plan view of the C-shaped retainer;

FIG. 9D is a top plan view of the assembled rod guide showing in stippled lines an outline of the C-shaped retainer inserted into the retaining structure of the clamp;

FIG. 9E is a perspective view of a C-shaped retainer being inserted into the retaining structure of the clamp, with the rod guide installed on a rod string;

FIGS. 10A to 10C are side views of a clamp portion of the rod guide being installed onto a rod string by engaging the clamshells of the clamp and axially aligning the clamshells with a slide hammer;

FIGS. 10D to 10E are side views of a bushing portion of the rod guide being installed onto the clamp portions by engaging the clamshells of the bushing and axially aligning the clamshells.

FIG. 10F is a side view of the rod guide with the clamp and bushings having been installed, and the C-shaped retainer being inserted into the retaining structure of the clamp;

FIG. 10G is a side view of the assembled rod guide with a retaining pin being inserted through the retaining structure and C-shaped retainer;

FIG. 11A is a top plan view of an embodiment of the rod guide with the bushing being secured to the clamp for rotation therewith, the bushing having helical ribs on the outer diameter thereof and axial splines on the inner diameter of the bushing to interface with corresponding groves in the outer diameter of the clamp;

FIG. 11B is a cross-sectional side view of the bushing according to FIG. 11A;

FIG. 11C is end view of the clamp clamshell portions according to FIG. 11C;

FIG. 12A is an end view of an embodiment of the clamp according to FIG. 11A, having grooves running along its outside diameter and parallel with the axis and compatible with the bushing of FIG. 11A;

FIG. 12B is a side view of the clamp of FIG. 12A;

FIG. 12C is a perspective view of the clamp of FIG. 12A.

FIG. 12D is a cross-sectional view of the clamp along D-D of FIG. 12B;

FIG. 12E is a cross-sectional view of the clamp along E-E of FIG. 12B;

FIG. 12F is a cross-sectional view of the clamp along F-F of FIG. 12B;

FIG. 13A is a perspective view of the bushing of FIG. 11 B;

FIG. 13B is an exploded view of the rod guide according to the clamp of FIG. 12C

FIG. 13C is an assembled view of a rod guide, absent the rod;

FIG. 14A is a top plan view of an embodiment of the rod guide with the bushing having ribs on its outside diameter running parallel with the axis of the rod guide;

FIG. 14B is a cross-sectional side view of the bushing of FIG. 14A;

FIG. 14C is a perspective view of the bushing of FIG. 14A;

FIGS. 15A and 15B are end and enlarged interlock interface views respectively of the guide with the center bore of each half of the clamp offset to the opposite side such that when the clearance in the interlock is taken up, the bore is round and a the same diameter as the rod;

FIGS. 16A and 16B are end and enlarged interlock interface views respectively showing the clamp in the locked position with the clearance taken up in the interlock and the center bore is now round.

FIG. 17A is a side view of a clamp illustrating an alternate embodiment of the interlocking interface;

FIG. 17B is a cross-sectional view of the clamp along B-B of FIG. 17A;

FIG. 17C is a cross-sectional view of the clamp along C-C of FIG. 17A;

FIG. 17D is a cross-sectional view of the clamp along D-D of FIG. 17A; and

FIG. 17E is an enlarged end view of the clamp along A-A of FIG. 17A.

DESCRIPTION

Turning to FIG. 1, a stator 10 of a PC pump 11 is fit to the bottom of production tubing 12 extending down a wellbore 14. A string of continuous rod 16 extends down the production tubing 12 and is driveably connected to the rotor 17 of the PC pump 11. A drive 20 at surface rotates the rod 16. The continuous rod string 16 is under tension as the reactive force of the pump forcing liquid uphole acts to pull downhole on the rotor 17 and thus, the rod 16.

Herein, rod guides 100,100 . . . are provided that can be installed on an intermediate section along the rod 16 without need for access to ends thereof and provides a synthetic, low friction surface for reduced contact to either the guide or surrounding tubing 12. Each rod guide 100 has a robust construction for secure attachment to the rod 16, yet is characterized by ease of installation. Each rod guide 100 can be installed periodically along the rod such as through a work window 21 installed above blow out preventer (BOP) or pack-off element of a wellhead. During run in of a string of PC pump's continuous rod 16 into production tubing, wellbore pressure can be controlled, and the work window 21 can be opened for access to the continuous rod and sequential installation of one or more guides 100,100.

As is relevant in wellbores 14 having a curve therein, such as at the heel of a horizontal well, the rod 16 is pulled up in tension against the uphole side of the curve of the tubing 12. It is advantageous to have rod guides 100,100 spaced along the rod 16 as the point of contact between the rod 16 and the production tubing 12, the rod guides 100 having interface materials of construction selected for minimizing contact wear therebetween.

With reference to FIGS. 2A and 2B, the rod 16 is a cylindrical member of circular cross section. Each of one or more rod guides 100 is a tubular device fit to the rod 16 intermediate its length.

With reference to FIG. 13B, each guide 100 comprises two main components: a tubular clamp 102, and a tubular bushing 104. The clamp 102 is secured to the rod 16 and the bushing 104 is retained to the clamp 102. The bushing 104 stands radially outwards from the clamp 102 so as to form the point of contact with the environment, such as the production tubing 12. In the production tubing 12 and PC pump scenario, the rod string 16 extends within the production tubing 12 and the bushing 104 engages the inside surface of the production tubing 12, minimizing wear therebetween. The bushing 104 is formed of a material softer than that of the tubing 12, such as plastics and other synthetic materials.

Further, the bushing 104 can be rotatable about the clamp 102 for further reduction in tubing wear. The rotatable bushing 104 is retained axially to the clamp 102. As discussed below, in other embodiments, the bushing 104 can also be non-rotatable and bonded to the clamp 102.

With reference to FIGS. 3A, 3B, and 3C the clamp 102 is a cylindrical tubular having a top end 192, bottom end 194, cylindrical inner rod bore 200 and a cylindrical outer bearing surface 202. In the depicted embodiment, the inner bore 200 and outer bearing surface 202 are concentric. The inner bore 200 is sized to correspond with the rod diameter. For example for a nominal 1″ diameter rod 16, the inner bore 200 is also about 1″.

For installation to a rod 16, intermediate its length, the clamp 102 is formed in two parts, a first clamshell clamp portion 208 a coupled to a second and opposing clamshell clamp portion 208 b. The clamshell portions 208 a and 208 b, are releaseably coupled at an interlocking interface. The interlocking interface implements complementary interlocking profiles 214 extending along a separation plane 204.

As discussed, the clamp is a split clamp having two clamshells 208 a, 208 b for enclosing the inner bore 200. Unlike most split clamps, each clamshell 208 a,208 b is not divided along the axis nor equally across the diameter.

Having reference to FIG. 3A instead, the interlocking between each clamshell 208 a, 208 b is along a separation plane 204, formed from one end of the clamp 102 to the other end and at an angle to the axis. The separation plane 204 is inclined from the axis so as to angle from one side of the axis 206 at one end of the guide 100, to the other side of the axis 206 at the other end of the guide 100. As shown in FIG. 3A, the separation plane 204 passes through the axis 206 at some point intermediate the ends. In other words, the separation plane 204 is neither parallel to, nor along the tubular axis 206. The separation plane 204 intersects the inner bore 20 at both opposing ends of the clamp 102 each clamshell having a chord of a recess formed therein so as to accept the cross-section of the rod 16. Thus, a disassembled clamp 102 can installed to any point along the rod 16, even rod ends are not accessible, or are so remote, so that end installation is not feasible.

Referring also to FIG. 4, the cross-section of the opposing and generally semi-circular segments 210 a,210 b adjacent either end are unequal in area , one being larger than the other; a larger segment 210 a having a central angle greater than 180° and a smaller segment 210 b having a central angle less than 180°.

During installation of one or the other of the clamshells to the rod 16, access to the full diameter of the inner bore 200 of the larger circular segment 210 a can be narrow and restricted, like a cove. The chord length or opening width W of the inner bore is less than that of the bore's diameter D. Line extensions drawn from tangents to the arc terminus of the circumference of the inner bore 200 of the larger circular segment 210 a will converge. Thus, the opening width W across the inner bore of the larger circular segment 210 a is less than that of the inner bore diameter D and in the case of close dimensional tolerance, the opposing small, encircling arc portions can interfere with the rod 16 and clamshell installation thereto if not removed such as by machining.

Correspondingly, the same opening width W across the inner bore of the smaller segment 210 b is also smaller than the diameter D, but as the central angle is less than 180 degrees, the remaining inner bore is not a hindrance but is shallow, such as an indentation or bay, and easily receives the rod diameter.

As shown in FIGS. 5A and 5B, the opening width W of the inner bore 200 varies from one end to the other, from a narrow cove opening WC at one end, passing through the diameter intermediate a height of the clamp, and a wider bay opening WB at the other. In manufacture, from one end and axially therealong, the otherwise interfering and partially encircling arc portions AP can be removed from the narrow cove opening WC at each end to widen the effective opening width along the separation plane 204 until equal to at least the rod diameter D entirely therealong.

The separation plane 204 forms two tubular wall faces 212,212 on each clamshell portion 208 a,208 b. The wall faces form the interlocking interface. Each wall face 212 is fit with an interlocking profile 214, such as a dovetail or similar joint to retain one clamshell radially to the other. The cross-section of the profile is consistent axially and the clamshells 208 a,208 b are assembled end-to-opposite end and are releaseably coupled by sliding them together and apart along the separation plane 204.

As shown in FIG. 10A, during assembly, the respective larger ends are aligned end-to-end. As best shown in FIG. 4, due to the angle of separation plane 204, the diametral extent or span S of the inner bore 200 across the opposing clamshells 208 a,208 b is initially greater than the nominal diameter D of the inner bore 200 and diminishes during axial coupling until the diametral extent or span S is that of the rod diameter D, delimited by the particular, in-the-field rod diameter.

Having reference to FIGS. 5A, 5B and 6A,6B, in an embodiment, the interlocking profile 214 comprises tongues and slots of a generally dovetail shape. One clamshell 208 b is fit with male tongues 216 of trapezoidal cross-section. FIGS. 6A and 6B illustrate the opposing clamshell 208 a is fit with female slots 218 of corresponding trapezoidal cross- section. The complementary angled shoulders of the tongue and slot, slidable along the wall face 212, but are prevented from separation perpendicular thereto, or radially with respect to the inner bore. Other interlocking profiles such as circular or hook-like tongues and slots can be used. Some assembly clearance 220 is provided between tongues 216 and slots 218, often conveniently provided by loss, or kerf, in the manufacturing process.

With reference to FIG. 15A, in a typical embodiment, the clearance 220 at the interface of the interlocking profile is about 0.01 inches given a rod bore 200 diameter of 0.875 inches, an outer bearing surface 202 diameter of 1.64 inches, and a rod guide height of 4 inches.

With reference to FIGS. 10A through 10C, assembled generally axially, “generally” as the wall faces 212 are angled from the axis, the interlocking profiles 214 of the uphole end of the one clamshell are aligned with the complementary interlocking profile 214 of the downhole end of the other clamshell. The clamshells 208 a,208 b are arranged on opposing sides of the rod 16, generally aligning the uphole and downhole ends of each clamshell section. The clamshells 208 a,208 b are poised for slidable engagement. The tongues 216 and slots 218 engage for sliding axially together, and in opposing relative directions. One clamshell is driven axially into the other with the interlocking profiles 214 coupled. One can see that if the assembly is restricted to one direction only, the interlocking profiles need only extend along a portion of the wall faces 212,212, such as the tongues extending from the wall 212 on the larger portion of one clamshell and slots formed in the wall 212 on the larger portion of the opposing clamshell.

The angle or slope of the separation plane 204 can be steep enough to be generally self-locking. Self-holding or self-locking is known for thread pitches, tapered hubs and the like wherein the frictional resistance is greater than incidental forces applied thereto. For conventional tapered hubs, slopes of radial-to-axial ratio of 6:1 (10 deg) are conventionally known to enable self-locking and design forces in operation do not release the taper. For conventional tapered shanks the slope is as low as angle is about 2-3 degrees to overcome large torque loads, as opposed to, self-releasing interfaces such as milling machine tapers having a both key/keyway direct rotational coupling and steeper slopes of about 3.5:1 or 16 degrees.

Here, Applicant has determined that a separation plane incline of about 10:1, or about 5 to 6 degrees relative to the axis of the clamp, strikes a balance between inducing self-locking when assembled and resisting operational forces and torque and yet permitting disassembly with applied axial removal forces.

In the case of the embodiment having a replaceable bushing 104 described in greater detail below, and for greater security, a transverse retainer 270 is also installed (see FIG. 9E), such as to retain the bushing 104 axially to the clamp 102, and can also lock the two clamshell sections axially together.

While the clamp portions 208 a,208 b are segments of opposing circular arcs, when assembled, the actual span S perpendicular to the separation plane 204 is less than the diameter D along the separation plane 204, thus providing some jamming tolerance for clamping. Further aiding interference, typically the unreeling and reeling of rod string 16, during running and pulling out of hole, results in sufficient diametral dimensional variation in the rod such that inner diameter is sufficient to ensure clamp retention. Further a thin face portion of the wall faces along the separation plane 204 can be removed so that, when assembled the span S is less than the diameter D of the inner bore 200.

Further, the inner bore 200 may be circular or non-circular, however it need not match the configuration of the rod 16, including for installation over rods 16 having non-circular cross sections. In the instance of generally semi-elliptical rod cross sections, the inner bore 200 could be circular and sized to the major diameter for full flexibility in rotational positioning or the inner bore 200 could also be generally semi-elliptical resulting in only two rotational orientations for installation.

While the clamp along may constitute the entire rod guide 100, being sufficient to engage the rod 16 at the inner bore and an outer tubing wall at an outside surface, it is usually a desire to provide a mechanically strong clamp at the rod interface and a resilient bushing at the outer interface.

Discrete Bushing

Accordingly, and returning to FIG. 2A and with further reference to FIGS. 8A and 8B, a discrete or replaceable bushing 104 is arranged about the clamp 102. A simple assembly of two semi-circular tubular sections 250,250 of bushing 104, detailed in FIGS. 7A and 7B, can be similarly and axially assembled over the assembled two clamshell clamp portions.

The bushing 104 has a top end 196 and bottom end 198, an inner bore 252 sized to fit concentrically over the outer bearing surface 202 of the clamp 102. The outer surface of the bushing 254 can be cylindrical, or incorporate profiles such as with generally axially extending, radial protuberances such as those used in known rod centralizer applications. The bushing 104 can be rotatable on the outer bearing surface 202 of clamp 102.

Again, like the clamp 102, the bushing 104 is split into bushing clamshell sections 250,250 to enable installation to the assembled clamp along any intermediate location of the rod 16, then installed or arranged axially over the clamp 102. As shown in FIGS. 7A-7B, a second separation plane 254 results in pairs of diametrically-spaced, tubular wall faces 256,256. Each wall face 256 is also fit with interlocking profiles 258, here shown as circular tongues 260 with corresponding grooves or slots 264.

As the diameter of the inner bore 252 of the bushing is known, being sized to fit the outer bearing surface 202 of the clamp 102, the separation plane can be aligned along the axis.

As shown in FIGS. 7A-7B, in an alternative to the guide embodiments' arrangement of one wall face bearing the tongue and the opposing wall face bearing the slot, a double tongue 260 and slot 264 arrangement can be used. A tongue 260 extends from each wall face and, further, a slot 264 is formed on each wall face. This optimizes use of the wall section and provides maximal coupling strength.

As the two bushing clamshell sections 250,250 are identical, and being manufactured of a more readily manipulated material of construction, such as plastic, polymers or other synthetics, there is an opportunity to extrude continuous lengths of semi-circular sections and cut off pairs of clamshells lengths for assembly together as a rod bushing for completing a rod guide.

Applicant has determined that a suitable bushing material for oil and gas operations is an internally-lubricated, thermoplastic or polymer exhibiting a low friction such as VESCONITE®, a product of Vesco Plastic Sales, Pty Ltd.

As shown in FIG. 8A, the tubular bushing 104 is slid over one end of the assembled clamp 102 and a retainer C-washer 270 is driven laterally into engagement with an end structure of one or both clamp clamshell portions 208 a,208 b to retain the bushing 104 axially thereto.

FIGS. 8A and 8B are plan and cross-sectional views respectively of the clamp 102 and bushing 104 assembled about the rod 16 and illustrate one form of interlocking profile between the clamshell portions of each of the clamp 102 and the bushing 104. As noted herein there are a variety of interlocking profiles which can be used.

Turning to FIGS. 9A, 9B, 9C and 9D, one can see that, assembled, and as shown in FIG. 9A, one of the clamp clamshell portions 208 a,208 b can have a greater axial height than the other to form an axially offset retaining structure 280, and one or both clamshells 208 a,208 b can have a flange 282 formed at the opposing end as a stop for the bushing 104. As shown in FIG. 9B, and with the bushing 104 shown in place, and at the retaining structure 280 opposing the flange end 282, a pair of opposing, transverse, and straddling slots 284 are formed into the clamshell wall portion either side of the inner bore 200 for complementary receipt of the arms 272,272 of a U-shaped retainer 270 of FIG. 9C. The spacing of the arms 272,272 can be sized slightly smaller than that of the spacing of the base of slots 284 of FIG. 9B and 9D for an interference fit. Further, as shown in FIGS. 9D and 9E, both the clamshell retaining structure 280 and the retainer 270 can have axial pin holes 286 formed therein and which overlap when assembled. Once the retainer 270 is laterally installed into the slots 284 in the retainer structure, the pin holes 286 align and a malleable pin 288 can be driven into each aligned pair of pin holes 286. Returning to FIG. 9A, the internal pin hole 286 a has a larger diameter and as the pin 288 is driven into the internal pin hole 286 a, the pin 288 deforms, retaining the pin 288 therein and securing the retainer 270 to the clamp 102.

Note that the clamp portion 102 self-locks to the rod 16 and the bushing 104 merely rotates, if at all, on the clamp 102. The bushing portion 104 need not be structural other than to remain tubular about the clamp 102 in service. Unlike, taper bushings or hubs, the bushing 104 herein does not act to secure or clamp an inner portion, therefore being free to rotate if desired.

Dimensionally, of course in a PC pumping situation, the overall cross-section of the bushing 104 would not block the production tubing 12, the wear surface 254 is such so as to maximize the flow area thereby to the maximal extent possible. Further, the bushings 104 would be spaced close enough to form the periodic points of contact to separate the continuous rod 16 from excessive contact with the production tubing 12.

Having reference to FIGS. 10A to 10G, during assembly, the clamp 102 is assembled about the rod 16, the bushing 104 is assembled about the clamp 102 and the retainer 270 is secured. While striking tools such as hammers and the like can be utilized, a form of slide hammer H, having an open side as shown in FIG. 10C can be employed. The slide hammer H of FIG. 10C is shown to employ one upstanding and semi-circular striking surface for engaging only one clamshell 208 a,208 b at a time. Further, the slide hammer H can be made of a non-sparking material to further enhance the safety of the installation and removal procedure.

A shown in FIGS. 10A and 10B, the two clamp clamshells 208 a,208 b are aligned axially and the interlocking profiles 214 aligned. The clamp clamshell ends 194,194 having the largest chord sections are aligned, forming the largest effective inner bore diametral extent, and the interlocking profiles are slidably assembled by hand as shown in FIG. 10B until friction or rod interference is too much to be overcome by hand.

In the illustration of FIG. 10C, the lower clamp clamshell 208 a is struck with the slide hammer H until the upstanding clamp clamshell 208 b stands above the other clamp clamshell portion 208 a. The clamp 102 is self-locking and will remain assembled. Similarly, the clamp 102 is easily removed by striking the top 192 of the other half of the clamshell 208 b to release the clamp 102.

Also as shown in FIGS. 10C and 10D, the bushing 104 is fit about the clamp 102 and assembled axially. As the parts are identical and semi-circular, there is no order or arrangement needed other than to align the interlocking profiles. As shown in FIG. 10D and 10E, either assembled above the clamp 102 or assembled about the clamp 102, the two bushing clamshells 250,250 are assembled and lowered to engage clamp flange 282. Resting on the flange 282, the uphole end of the bushing 104 is short of the retainer slots 284 in the clamp and the retainer 270 can be installed thereto and the malleable pins 288 hammered into place in the pinholes 286 (FIGS. 10F and 10G), axially retaining the bushing 104 sandwiched between the flange 282 and the retainer 270.

With reference to FIGS. 11A to 13C, in another embodiment, the bushing 104 can bonded to the outer surface of the clamp 102 with an adhesive or through vulcanization and therefore rotates with the clamp 102. In this embodiment, the retainer 270 and retaining structure 280 are not required to couple the bushing and clamp. As such, this embodiment is simple in design and less expensive to manufacture. As in this embodiment there is no retainer, or retaining structure, to further secure the bushing 104 to the clamp 102, a separation plane 204 through both the clamp 102 and the bushing 104 is provided, again at a plane incline of about 10:1. The bonded bushing configuration can be used on a regular sucker rod as well as a continuous rod.

To further aid in bonding and resisting operational torque, grooves 302 can be incorporated on the outer bearing surface of the clamp 102 which mate with corresponding splines 304 set in the inner bore 252 of the bushing 104. In another embodiment, splines can be incorporated on the outer bearing surface of the clamp 102 which mate with corresponding grooves set in the inner bore 252 of the bushing 104. The splines 304 can run along the axial length of the bushing 104, and the grooves 302 along the axial length of the clamp 102. The addition of the grooves 302 and splines 304 increases the bonding surface area between the interface of the clamp 102 and bushing 104, and also resists failure of the bond when the rod 16 undergoes rotation. The bushing portion need not incorporate an angled interlocking interface to grip the clamp at its inner bore. The bushing need only be assembled to form a tubular or known diameter.

As shown in FIGS. 12A through 12E, the angled separation plane results in a different chord across the clamp along its height.

Several outer profiles can be used for the bushing 104. As an example, and as best illustrated in FIGS. 13A and 14A to 14C, bushing ribs 310 can extend helically or extend parallel with the axis of the bushing respectively. Such configurations maintain some open cross-sectional annular area for free flow of fluids about the rod 16 and production tubing 12.

As introduced above, the interlocking interface can be manufactured in several ways, including numbers and shape of interface interlocking profiles.

To avoid material waste in the manufacturing of each clamshell 208 a or 208 b from discrete based stock material, the use of wire electrical discharge machining (wire EDM) permits manufacture of both clamshell portions from a one piece of round stock or other base blank. The use of a wire tool electrode permits the precise formation of the interlock profile. The inner bore and separation interface is is also wire EDM cut. As shown in FIGS. 15A and 15B, the center for the cut is offset to the left to cut the right side and offset to the right to cut the left side. This resulting tolerance results in a round bore as shown in FIGS. 16A and 16B when the clearance in the taper cut separation plane is taken up when assembled. This allows one to manufacture a clamp from one workpiece.

Further, the partially encircling arc portions AP can also be easily removed from the narrow cove opening at the large ends to widen the effective opening width along the separation plane 204.

With reference to FIGS. 17A through 17E another interlocking profile comprises a hook-to-hook interface. With reference to the larger view of FIG. 17E, the hooks 222 extend tangentially, then radially to generally align with the separation plane 204 so as resist separation normal to the separation plane 204. Compared to the “dovetail” tongue and fully formed trapezoidal slot, having only one complementary angled hook shoulder, this interlock permits one to make a thinner walled clamp and allowing more bushing or wear material. 

What is claimed is:
 1. A rod guide for installation on a rod string comprising: a tubular clamp having an inner rod bore and an outer bearing surface about an axis and having an axial height, the clamp being split diametrically along a first separation plane through the rod bore to form a first clamshell clamp portion and a second clamshell clamp portion, the first separation plane extending along the rod bore at an angle to the axis and passing through the axis intermediate the axial height for forming a pair of radial wall faces extending axially along the height of each of the first and second clamshell clamp portions; and interlocking clamp profiles along at least a portion of each of the wall faces and complementary between the first and second clamshell clamp portions for radially securing the clamshell clamp portions together.
 2. The rod guide of claim 1 further comprising a bushing having an inner bushing bore fit to the clamp's outer bearing surface and an outer wear surface and having an axial height, the bushing being split diametrically along a second separation plane through the inner bushing bore to form a first clamshell bushing portion and a second clamshell bushing portion, the second separation plane extending along the inner bushing bore for forming a pair of radial bushing wall faces extending axially along the height of each of the first and second clamshell bushing portions; and interlocking bushing profiles along at least a portion of each of the bushing wall faces and complementary between the first and second clamshell bushing portions for radially securing the clamshell bushing portions together.
 3. The rod guide of claim 1 wherein each interlocking clamp profile comprises a complementary dovetail tongue and slot.
 4. The rod guide of claim 1 wherein: each of the pair of wall faces of the first clamshell clamp portion comprises a tongue along at least a portion of its height; and each of the pair of wall faces of the second clamshell clamp portion comprises a slot along its height, the tongues being axially slidable along the slots and complementary for locking the clamshell clamp portions together radially.
 5. The rod guide of claim 2 wherein each interlocking bushing profile comprises a complementary circular bushing tongue and bushing slot.
 6. The rod guide of claim 5 wherein: each of the pair of bushing wall faces of the first clamshell bushing portion comprises a bushing tongue along at least a portion of its height; and each of the pair of bushing wall faces of the second clamshell bushing portion comprises a bushing slot along its height; the bushing tongues being axially slidable along the bushing slots and complementary for locking the clamshell bushing portions together radially.
 7. The rod guide of claim 5 wherein: each of the pair of bushing wall faces of the clamshell bushing portions comprises a bushing tongue along at least a portion of its height and a bushing slot along its height; the bushing tongues being axially slidable along the bushing slots and complementary for locking the clamshell bushing portions together radially.
 8. The rod guide of claim 1 wherein the first separation plane angle is self-locking.
 9. The rod guide of claim 1 wherein the first separation plane angle is greater than about 2 degrees and less than about 16 degrees.
 10. The rod guide of claim 1 wherein the first separation plane angle is between about 5 to about 6 degrees.
 11. The rod guide of claim 2 wherein the second separation plane is parallel to, and along, the axis of the bushing bore.
 12. The rod guide of claim 2 wherein the second separation plane is at an angle to the axis and passes through the axis intermediate an axial height of the bushing.
 13. The rod guide of claim 12 wherein the second separation plane angle is self-locking.
 14. The rod guide of claim 2 wherein the bushing is made of a low friction polymer.
 15. The rod guide of claim 2 wherein at least one of the clamshell clamp portions comprise a flange at a first end.
 16. The rod guide of claim 15 wherein one of the clamshell clamp portions is of a greater height than the opposing clamshell clamp to form an axially offset retaining structure at a second end and having slots formed therein to receive a retainer and sandwich the bushing between the flange and the retainer.
 17. The rod guide of claim 16 wherein the retainer is a C-shaped retainer.
 18. The rod guide of claim 16 wherein the retaining structure and retainer each include one or more complementary pinholes for receiving retaining pins.
 19. The rod guide of claim 18 wherein the one or more pinholes of the retaining structure are smaller in diameter than the one or more pinholes of the retainer.
 20. The rod guide of claim 16 wherein the bushing is rotatable about the clamp.
 21. The rod guide of claim 1 further comprising a bushing having an inner bushing bore fit to the clamp's outer bearing surface and an outer wear surface, wherein the bushing is bonded to the clamp's outer bearing surface.
 22. The rod guide of claim 21 wherein at least one clamp groove runs axially along the outer bearing surface of the clamp and at least one bushing spline complementary to the at least one clamp groove runs axially along the inner bushing bore.
 23. The rod guide of claim 2 wherein a plurality of bushing ribs extend generally axially along the outer wear surface of the bushing.
 24. A method for securing a rod guide to a string of rod, comprising: locating a first clamshell clamp portion about the rod; locating a second clamshell clamp portion in opposing relation about the rod, the first and second clamshell clamp portions having an inner bore and interlocking interfaces along a first separation plane through the inner bore, the first separation plane at an angle to the rod's axis; arranging a first end of one of the first or second clamshell clamp portions with an opposing end of the other of the second or first clamshell clamp portion; aligning the interlocking interfaces of the respective interlocking interfaces of the first or second clamshell clamp portions; axially and slidably coupling the first and second clamshell clamp portions until the first or second clamshell clamp portions clamp to the rod.
 25. The method of claim 24, further comprising locating a first clamshell bushing portion about the outer bearing surface of the first and second clamshell clamp portions; locating a second clamshell bushing portion in opposing relation about the first and second clamshell clamp portions; coupling the first and second clamshell bushing portions; and axially restraining the first and second clamshell bushing portions to the first and second clamshell clamp portions.
 26. The method of claim 24, further comprising using a striking tool to strike one of the first or second clamshell clamp portions to axially and slidably couple the first or second clamshell clamp portion with the second or first clamshell clamp portion.
 27. The method of claim 25, wherein the axially retaining step comprises sandwiching the first and second clamshell bushing portions between a flange and a retainer by inserting a retainer into a retaining structure of the first or second clamshell clamp portion and aligning a one or more retaining pin holes of the retaining structure with a one or more pin holes of the retainer to secure the clamshell bushing portions to the clamp. 